The present invention relates to a fuel injection valve for an internal combustion engine, and more particularly to a fuel injection valve using a stacked piezoelectric ceramics displacement magnifying device as an valve actuator.
The stacked piezoelectric ceramics is constituted of a plurality of stacked ceramics elements displaceable upon application of an electric field thereto. The amount of displacement (distorsion) of the stacked ceramics elements varies with the strength of electric field. As the product of the displacement and a force generated is relatively large, and responsiveness is remarkably high, the stacked piezoelectric ceramics is used as a high-responsive actuator in various fields.
However, the amount of displacement of the stacked piezoelectric ceramics is small, and therefore, an actuator having the stacked piezoelectric ceramics combined with a displacement magnifying device is being developed. Such an piezoelectric actuator including a displacement magnifying device is described in SAE Technical Paper Series No. 800502 Page 10, FIG. 16 and Proceedings of the 5th Meeting on Ferroelectric Materials and Their Applications (1985) 30-V-2, for example. There have been proposed three types of the displacement magnifying device as shown in FIGS. 4 to 6.
Referring to FIG. 4 which shows a first type of the displacement magnifying device, a flexing member 1 is formed of an elastic strip which is easily flexible in a horizontal direction shown, but is hardly expandable in a vertical direction shown. The flexing member 1 is installed under a preliminarily flexed condition as shown. When the flexing member 1 under the condition is pulled vertically by a stacked piezoelectric ceramics, a central portion of the flexing member 1 is greatly displaced in the horizontal direction.
Referring to FIG. 5 which shows a second type of the displacement magnifying device, levers 6 and 7 are connected through hinges 4 and 5 to a fixed member 3, respectively. The levers 6 and 7 are connected with each other through a hinge 8. When the lever 6 is upwardly urged by a stacked piezoelectric ceramics 2, the lever 7 is rotated clockwise about the hinge 5. Accordingly, an upper end of the lever 7 is greatly displaced.
Referring to FIG. 6 which shows a third type of the displacement magnifying device, pistons 9 and 10 are inserted into two cylinders connected to each other and having different sectional areas, and an uncompressible hydraulic fluid F is filled in a space between both the pistons 9 and 10. When the piston 9 having a larger sectional area is urged by a stacked piezoelectric ceramics 2, the piston 10 having a smaller sectional area is greatly displaced.
However, in the case that the conventional displacement magnifying device using the stacked piezoelectric ceramics is used for the actuator of the fuel injection valve, the construction of the displacement magnifying device is required to be compact and elongated along an output displacement axis in accordance with a cylindrical configuration of the fuel injection valve having a valve body at a front end portion thereof. In the first type device as shown in FIG. 4, the length of the flexing member 1 cannot be sufficiently ensured, and a large magnification ratio cannot be obtained. In the second type device as shown in FIG. 5, a displacement output point is positioned at an edge of the device, and therefore, a displacement magnifying function cannot be sufficiently provided. In the third type device as shown in FIG. 6, the length of the device along the output displacement axis is large, and precise working is required, causing increased costs. Further, the hydraulic fluid F tends to vaporize at high temperatures, thereby hindering a valve operation.